Chemotherapy and radiation exposure are currently the major options for the treatment of cancer, but the utility of both these approaches is severely limited by adverse effects on normal tissue, and the frequent development of tumor cell resistance. It is therefore desirable to improve the efficacy of such treatments in a way that does not increase the toxicity associated with them. One way to achieve this is by the use of specific sensitizing agents such as those described herein.
An individual cell replicates by making an exact copy of its chromosomes, and then segregating these into separate cells. This cycle of DNA replication, chromosome separation and division is regulated by mechanisms within the cell that maintain the order of the steps and ensure that each step is precisely carried out. Involved in these processes are the cell cycle checkpoints (Hartwell et al., Science, Nov. 3, 1989, 246(4930):629-34) where cells may arrest to ensure DNA repair mechanisms have time to operate prior to continuing through the cycle into mitosis. There are two such checkpoints in the cell cycle—the G1/S checkpoint that is regulated by p53 and the G2/M checkpoint that is monitored by the Ser/Thr kinase checkpoint kinase 1 (CHK1).
The cell cycle arrest induced by these checkpoints is a mechanism by which cells can overcome the damage resulting from radio- or chemotherapy, their abrogation by novel agents should increase the sensitivity of tumor cells to DNA damaging therapies. Additionally, the tumor specific abrogation of the G1/S checkpoint by p53 mutations in the majority of tumors can be exploited to provide tumor selective agents. One approach to the design of chemosensitizers that abrogate the G2/M checkpoint is to develop inhibitors of the key G2/M regulatory kinase CHK1, and this approach has been shown to work in a number of proof of concept studies. (Koniaras et al., Oncogene, 2001, 20:7453; Luo et al., Neoplasia, 2001, 3:411; Busby et al., Cancer Res., 2000, 60:2108; Jackson et al., Cancer Res., 2000, 60:566).